This invention relates generally to devices for carrying a cutting and drilling tool and other components for use in delayed coking reactor operation, and more particularly to the use of non-metallic belts that provide a fail-safe lifting design for raising and lowering such components.
In conventional petroleum refining operations, crude oil is processed into gasoline, diesel fuel, kerosene, lubricants or other useful materials through distillation or related means. In such an operation, the crude oil (which is typically subjected to various upstream processing or production steps at or near the well from which the oil is extracted) is heated to elevated temperatures in a fractional distillation unit in order to selectively release—depending on differing boiling points—the valuable volatile hydrocarbon components contained therein. The heavy remaining oils are drained from the fractionation unit, heated, and transferred into vessels (known as coke drums) at a temperature (specifically, a thermal cracking temperature) sufficient to drive off the remaining volatile materials to leave the drums full of solid coke. Because large-scale refineries can produce as much as 2,000 to 3,000 tons per day of solidified coke, the drums—which are as large as 30 feet in diameter and 140 feet in height—must be frequently cleared to make room for the next incoming batch.
One method of breaking up the coke residue is by using a decoking (or coke cutting) tool in conjunction with a decoking fluid, such as high pressure water. The tool (which is typically secured to a tower that is in turn mounted onto a support structure that surrounds the coke drum) is lowered into the coke drum through an opening in its top, and the high pressure water supply is introduced into the tool so that it can be selectively routed through—depending on the mode of operation—either the drilling or cutting nozzles of the tool to impinge on the coke in the drum and act as a coke-breaking fluid jet. Such tools require high flow rates and pressures (for example, flows of 1000 gallons per minute (gpm) at 3000 to 4000 pounds per square inch (psi) or more). Moreover, the tower, tool and its ancillary equipment (including among others drill stems, drive mechanisms, water-filled hoses or related conduit, collectively referred to as a cutting train that can be supported by a crosshead) can be extremely heavy, weighing (depending on the size and configuration) up to 15,000 pounds or more. A steel cable operated by a winch is used to raise or lower the cutting train. In addition, separate fall arresting gear is required in numerous decoking tool crosshead designs to prevent a freefall in the event of a cable break or a winch failure within the tower; such redundancy adds significantly to the maintenance and operation complexity, as well as the weight and cost of the decoking system without contributing to the efficiency of the actual decoking process.
To avoid having complex support structures for movement of the water jet cutting head and related equipment through the vertical entirety of the coke drums, a self-climbing crosshead-based lifting configuration may be employed, an example of which is depicted in U.S. Pat. No. 6,050,277 (the '277 patent) that is owned by the Assignee of the present invention and incorporated herein by reference in its entirety; such a configuration forms a crosshead drive system. An additional way that redundancy and complexity is avoided in the '277 patent is through the use of rollable carriages (such as those depicted in FIG. 3B thereof) on a track or rail so that a single tower (rather than multiple towers) that is used to support the cutting train can be transported between adjacent drums.
Despite the improvements made by such a configuration, difficulties remain. For example, the long lengths of the rack-and-pinion configuration must still rely upon rigid support by a vertical member that—while not as cumbersome as a complete tower—must be robust enough to ensure that precise engagement of their meshing gear teeth of the self-propelled drive system is maintained, as misregistration between them can lead to faulty (or no) crosshead movement; such rigidity can exact significant weight, cost and complexity tolls. Moreover, if a metallic wire cable (also called rope) is used to couple the cutting train to a set of counterweights over a corresponding set of pulleys in an attempt to permit the use of a smaller motor, significant additional weight (often 5000 to 8000 pounds or more) may be present.